Universal integrating accelerometer



Dec. 28, 1965 M. BRACUTT UNIVERSAL INTEGRATING ACGELEROMETER Filed Oct. 31, 1963 6 Sheets-Sheet 1 d 79 INVENTOR.

MICHAEL BRACUTT |o Bm ml ATTOR NEYS.

Dec. 28, 1965 cu 3,226,503

UNIVERSAL INTEGRATING ACCELEROMETER Filed 001.. 51, 1963 6 Sheets-Sheet 2 ea 34 I7 0 I INVENTOR. 27 26 MICHAEL BRACUTT 7%; 51 I 1. 9 M ANTORNEY-i Dec. 28, 1965 cu 3,226,503

UNIVERSAL INTEGRATING ACCELEROMETER Filed Oct. 51, 1963 6 Sheets-Sheet 5 INVENTOR. MICHAE L BRACUTT- BY m, W Q4 ATTORNEY!- Dec. 28, 1965 M. BRACUTT 3,226,503

UNIVERSAL INTEGRATING ACCELEROMETER Filed Oct. 51, 1965 6 Sheets-Sheet 4 Fig 7 Fig 8 42 i E INVENTO R.

42 MICHAEL BRACUTT BY if ml j J 7 WWW w 1 PM ATTORNEY).

UNIVERSAL INTEGRATING ACCELEROMETER Filed Oct. 31, 1963 6 Sheets-Sheet 5 INVENTOR. M ICHAEL BRACUTT Dec. 28, 1965 BRACUTT v 3,226,503

UNIVERSAL INTEGRATING ACCELEROMETER Filed Oct. 51, 1965 6 Sheets-Sheet 6 INVENTOR. MICHAEL BRACUTT BY fi m/g, m. XWM 1 mg kffi'sw W ATTORNEYS.

United States Patent 3,226,503 UNIVERSAL INTEGRATING ACCELEROMETER Michael Bracutt, Short Hills, N.J., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Army Filed Oct. 31, 1963, Ser. No. 320,589 Claims. (Cl. 20061.45)

This invention relates to integrating accelerometers such as are adapted for use on missiles and the like. It provides an integrating accelerometer which functions to complete an electric circuit when it is subjected to a predetermined maximum acceleration along its sensitive axis and automatically resets itself following its actuation by an acceleration below such maximum acceleration.

The integrating accelerometer of the present invention is a velocity sensing device which employs a flywheel integrator to sense linear acceleration along the sensitive axis of the accelerometer. When the velocity resulting from such acceleration reaches a predetermined value, closure of an electric circuit is elfected. The accelerometer includes a flywheel and gear train assembly, acting as a seismic mass, mounted on a guide rod with the low speed pinion of the gear train in mesh with a stationary rack and the high speed pinion of the gear train fixed to the flywheel shaft.

The flywheel includes a centrifugal switch-ing mechanism which is designed to operate as a function of the flywheel angular velocity. Flywheel angular velocity is proportional to missile velocity. This switching mechanism includes no mechanical springs but utilizes magnetic forces to establish the operational threshold. A bias and reset unit acts upon the seismic mass through a braking mechanism which decelerates the flywheel while the seismic mass is being returned to the zero position. This functions to erase the sensor (flywheel) velocity if the missile acceleration falls below the bias level before the predetermined velocity setting is reached.

The invention will be better understood from the following description when considered in connection with the accompanying drawings and its scope is indicated by the appended claims.

Referring to the drawings:

FIGS. 1 and 2 show the accelerometer with the casing removed and with the various parts in their unarmed positions,

FIG. 1A, is a similar view with the biasing mass reset assembly removed,

FIG. 3 is similar to FIG. 1 with the exception that the various parts are in their armed positions,

FIG. 4 is a side view of the seismic mass and gear train assembly,

FIG. 5 is a view taken on the line 5-5 of FIG. 4,

FIG. 6 is a top view of the gear train,

FIGS. 7 and 8 are different views of the biasing mass reset assembly,

FIG. 9 is a side view of the flywheel assembly,

FIG. 10 is a section taken on the line 10-10 of FIG. 9,

FIGS. 11 to 13 illustrate various features of the switch actuating mechanism,

FIG. 14 shows the arrangement of the flywheel brake mechanism, and

FIG. 15 illustrates certain features of the flywheel.

As indicated by FIGS. 1 to 3, the accelerometer includes a base 10 from which extends an upright 11. Also extending upwardly from the base 10 are a gear rack 12, a guide rod 13 and a tube 14 which constitutes part of a biasing mass and reset assembly. A cross-piece 15 is fixed to the upright 11, to the rod 13 and to the tube 14. Arranged to move along the rod 13 are a gear train 16, which may be changed to accommodate missiles of varying acceleration characteristics, and a contact and flywheel assembly 17, such movement being elfected by accelera- 3,226,593 Patented Dec. 28, 1965 tion of the accelerometer in a direction upwardly from the base 10. As the gear train and flywheel assemblies move along the rod 13, the low speed pinion of the gear train is driven by the rack 12 and the gear train functions to rotate the flywheel assembly about the flywheel shaft 18. The relation between these various parts is better seen in FIGS. 4 to 6.

FIGS. 4 to 6 show an input shaft 19 which is driven from the rack 12 (FIGS. 1 to 3) through a pinion 20 and is journaled in roller bearings 21 and 22. Fixed to the input shaft 19 is a pinion 23. This pinion functions through a gear train 242526-2728-2930 to drive the output shaft 18 to which the flywheel 17 is fixed,

Between gears 28 and 29 is a spring clutch 31. These two gears have hubs which meet midway and are machined to a slight interference fit to the inside of the spring. The purpose of this clutch is to allow the seismic mass to drive the flywheel in one direction only and to allow the flywheel to free-wheel when resetting the mass to Zero position. Also the seismic mass can bottom without damage to the gear train since there is no sudden braking of the flywheel which continues to spin. The friction between the seismic mass and its guide rod 13 is made very low by means of a linear ball bearing bushing 32. This type of bushing introduces a ball bearing action by means of a system of circulating balls.

A pin 33 (FIGS. 5 and 14) is a pivot for a brake shoe 43 which acts on the flywheel 17. When the bias unit 14 (FIG. 1) operates to release the seismic mass, the brake shoe is forced away from the flywheel by a spring 34.

The bias and reset unit is illustrated by FIGS. 7 and 8. This unit functions to (1) provide a bias level of acceleration below which the accelerometer does not operate, (2) reset the seismic mass when the acceleration falls below the bias level and (3) reset the seismic mass after manual operation. It includes a bias mass 35 which slides inside the tube 14 (FIGS. 1 and 7) and is held in its illustrated Zero position by the spring 34 (FIGS. 1, 5, 7 and 8). A pin 36 is attached to the bias mass 35 by means of a set screw 37 and projects across the two sides of the tube 14 through clearance slots 38 and 39. One end of the pin 36 is attached to the spring 34. The other end of this pin functions as hereinafter described to release a brake shoe which is spring biased against the flywheel 17. The spring 34 is mounted 011 a barrel 40 which is held in place by a retaining ring 41. The ends of the tube 14 are closed by caps 42 so that the mass 35 is cushioned by air pockets at each end of the stroke. This eliminates damage when the unit is subjected to shock and vibration.

As shown in FIG. 14, the brake mechanism includes the brake shoe 43 which has one end fixed to the pin 33 and the other arranged to engage the periphery of the flywheel 17. The pin 33 is pivoted in an extension of a gear block 44 and has fixed to its other end a cam-shaped member 47 which is biased by a spring 48 to a position such that the brake shoe 43 is disengaged from the flywheel 17. Working against the spring 48 is the spring 34 which functions through the pin 36 (FIG. 7) to force the brake shoe against the flywheel so long as the mass 35 is in the position illustrated by FIG. 7. Upon downward movement of the mass, however, the pin 36 is disengaged from the cam-shaped member 47 and the brake shoe is disengaged from the flywheel by the spring 48.

The weight of the bias mass 35 (FIG. 7) and the force of the bias spring 34 set the bias level in gs at which the accelerometer operates. As missile acceleration exceeds the bias level, the movement of the bias mass results in release of the brake on the flywheel and permits free travel of the seismic mass. When acceleration falls below the bias level, the bias mass 35 resets the seismic mass to zero position and, at the same time, applies the brake shoe to the flywheel.

The various features of the flywheel assembly are shown in FIGS. 9 to 15. As best shown in FIG. 15, the flywheel includes a segmented structure of two magnets 49 and 50, soft iron pole pieces 51 and 52, and a brass center piece 53. Circular grooves 54 and 55 (FIG. 11) are cut into the structure so that plungers 56 and 57 can rotate about two centers 58 and 59 (FIG. 9). Fixedto the plunger 56 by means of a pin 60 (FIG. 10) is a sector gear 61. A similar sector gear 62 is fixed to the plunger 57. These two sector gears mesh with a central pinion 63.

The two sector gears 61 and 62 are linked together by the pinion 63. This provides a balanced linkage which maintains the structure insensitive to all acceleration forces except that due to the spin of the flywheel. As a result, missile acceleration in any sidewise direction, any shock or any vibration has no eflect on the velocity pickoff.

When the flywheel is rotated to a speed where the centrifugal force exceeds the magnetic attraction, the plungers 56 and 57 separate from the soft iron center piece 64. As this occurs, the airgap in the magnetic circuit is increased reducing the holding force. At the same time, the centrifugal force increases as gravitational centers of the plungers move outwardly. By means of the various ball bearings indicated in the drawings, friction is minimized so that breakaway occurs at a precise rotational speed without restraint that may vary with friction.

The switching mechanism is actuated by rotation of the pinion 63. A pin 65 projecting from the face of the pinion and passing through a clearance slot in a contactor 67 engages a barrier plate 66 and causes it to rotate. The contactor 67 carries two contacts 68 and 69 on a spring member and at each end of this member are guide pins 72 and 73 for preventing rotation of the contactor with respect to the flywheel. The pin 65 engages the barrier plate 66 but no rotation of the contactor 67 occurs until after 15 degrees of rotation so that there is no frictional restraint to the centrifugal mechanism at breakaway and also so that the mechanism may attain momentum to more effectively rotate the barrier plate 66.

The barrier plate 66 is made of non-conducting mateterial and is located between the contactor 67 and a fixed plate 74 (FIG. 2). The contacts 68 and 69 are spring loaded against the non-conducting barrier plate 66. There are two holes in this plate normally positioned at an angular distance from the contacts 68 and 69. When the barrier plate 66 is rotated by the pin 65, however, these holes uncover the contacts and allow them to pop through into contact with the conductive rings 70 and 71 (FIG. 12). These rings are printed circuits on a non-conducting base which is bonded to the plate 74 which is attached to the seismic mass. As indicated in FIGS. 2 and 12 the rings 70 and 71 are connected to output terminals 75 and 76. A normally closed monitor switch 77 is connected to terminals 78 and 79 is utilized to indicate electrically that the seismic mass is in its zero position. Its contacts open when the mass moves away from this position. In its closed position it completes the circuit of an indicator which is connected to terminals 78 and '79.

The operation of the accelerometer is initiated and effected by acceleration in the direction of flight. When the device is accelerated in the direction of flight, the seismic mass is subject to a force tending to drive it in the opposite direction. If the acceleration is above the limit established by the preload of the bias spring 34, the

bias mass 35 moves inside the cylinder 14 and releases the brake shoe 43 from the flywheel so that the seismic mass is free to move along the direction of the sensitive axis. Thus the seismic mass is forced to move toward the base 10. This causes the flywheel 17 to rotate on its axis. As can be readily established by a mathematical analysis, the flywheel angular velocity is a measure of the first time integral of the linear acceleration experienced along the sensitive axis of the accelerometer. When the flywheel reaches an angular velocity that is equivalent to the desired velocity, a centrifugal force is developed to overcome the magnetic attraction on the plungers 56 and 57 in the flywheel. These plungers operate through sector gears 61 and 62, pinion 63 to engage contacts 68 and 69 with conductive rings 70 and 71. These contacts remain closed until reset manually. This is done by deflecting the contactor 67 until the contacts 68 and 69 clear the barrier plate 66. Then the barrier plate is free to be returned to its normal position. Since the centrifugal force is zero, the plungers 56 and 57 are attracted to the center shunt, and the barrier plate is returned to its standby position.

When the contacts close, the friction between the contacts and the printed rings bring the flywheel to rest. When the acceleration falls below the bias level, the seismic mass is returned to zero position with the contacts closed. This is eflected with little restraint by means of the one-way spring clutch 31.

If, for any reason, acceleration ceases or falls below the bias level after the seismic mass has left its starting position but before operation has occurred the reset spring 34 will return the mechanism to zero position. Another characteristic of the mechanism is that whenever acceleration, after starting, falls below the bias level, the brake is applied to the flywheel and so erases most of the velocity measured. In this way, if acceleration should be resumed to a value above the bias value, full velocity is not likely to be measured and hence, such a mal-function missile will not cause final switch closure.

Still another advantage of the mechanism is the eifectiveness with which the small reset mass can bring to rest the relatively larger seismic mass with high reflected flywheel inertia. This is because of the force multiplying effect of the brake acting on the high speed low torque shaft on which the flywheel is mounted.

I claim:

1. In an integrating accelerometer, the combination of a supporting structure including a base,

a gear rack, mounted upright on said base,

a guide rod mounted upright on said base in spaced parallel relation to said gear rack,

a seismic mass including a step-up gear train, a flywheel,

centrifugal switching mechanism carried by said flywheel and operable to complete a control circuit connection upon a predetermined rotational speed of said flywheel, said mechanism having centrifugallymovable magnetic means for establishing an operating threshold, said mass being mounted on and movable along said guide rod upon acceleration of said mass in a direction normal to said base and axially of said guide rod, said gear train having a low speed pinion in mesh with said rack and a high speed pinion rotatable with said flywheel to drive said flywheel at an angular velocity proportional to a desired acceleration rate and velocity,

means mounted on said base and including a spooled retracting spring for resiliently maintaining said mass in a zero position spaced from said base on said rod when the acceleration of said accelerometer is below a predetermined bias level and for resetting said mass to said zero position when said acceleration falls below said bias level, and

a brake shoe biased into engagement with 'said flywheel and releasable therefrom through contact with said last-named means upon movement of said mass from said zero position.

2. In an integrating accelerometer, the combination of a supporting structure including a base,

a gear rack mounted upright on said base,

a guide rod mounted upright on said base in spaced parrallel relation to said gear rack,

a seismic mass including a step-up gear train and a flywheel,

a centrifugal switching mechanism carried by said flywheel and operable to complete a control circuit connection upon a predetermined rotational speed of said flywheel,

said mechanism having centrifugally-movable magnetic means for establishing an operating threshold,

said mass being mounted on and movable along said guide rod upon acceleration of said mass in a direction normal to said base and axially of said guide rod,

said gear train having a low speed pinion in mesh with said rack and a high speed pinion rotatable with said flywheel to drive said flywheel at an angular velocity proportional to a desired acceleration rate,

means mounted on said base and including a spool retracting spring for resiliently maintaining said mass in a zero position spaced from said base on said rod when the acceleration of said accelerometer is below a predetermined bias level and for resetting said mass to said zero position when said acceleration falls below said bias level,

a brake shoe biased into engagement with said flywheel and releasable therefrom through contact with said last-named means upon movement of said mass from said zero position,

a monitor switch having operating means to effect closure thereof only when said mass is in the zero position, and

a spring clutch in said gear train for allowing said flywheel to free wheel when resetting said mass to its zero position.

. In an integrating accelerometer the combination of supporting structure including a base,

gear rack mounted upright on said base,

guide rod mounted upright on said base in spaced parallel relation to said gear rack,

a seismic mass including a step-up gear train and a flywheel,

a centrifugal switching mechanism carried by said flywheel and operable to complete a control circuit connection upon a predetermined rotational speed of said flywheel,

said mass being mounted on and movable along said guide rod upon acceleration of said mass in a direction normal to said base and axially of said guide rod, said gear train having a low speed pinion in mesh with said rack and a high speed pinion rotatable with said flywheel to drive said flywheel at an angular velocity proportional to a desired acceleration rate,

means mounted on said base and including a spool retracting spring for resiliently maintaining said mass in a zero position spaced from said base on said rod when the acceleration of said accelerometer is below a predetermined bias level and for resetting said mass to said zero position when said acceleration falls below said bias level,

a brake shoe biased into engagement with said flywheel and releasable therefrom through contact with said last-named means upon movement of said mass from said zero position,

a pair of magnetic plungers in said switch mechanism and held to a center in said flywheel by magnetic attraction and movable outwardly from said center by a predetermined angular velocity of said flywheel,

a pair of sector gears rotatable by said outward movement,

a rotatable shaft having at one end a pinion in mesh with said sector gears and at the other end a switch contractor, and

means for delaying the completion of said control circuit connection by said contactor for a predetermined time interval following said outward movement.

4. An integrating accelerometer, of the velocity-sensing type, comprising in combination,

a flywheel mounted on a rotatable shaft,

a gear train assembly acting with the flywheel as a seismic mass,

a supporting structure including a base,

a fixed guide rod for said seismic mass mounted up- 5 right on said base for axial alignment with the direction of acceleration in operation,

a gear rack mounted on said base in parallel spaced relation to said guide rod,

said gear train having low-speed pinion in mesh with said gear rack and a high-speed pinion connected with said flywheel shaft to drive said flywheel in response to movement of said seismic mass along said guide rod and in mesh with said rack,

a centrifugal switching mechanism carried by said flywheel for operation at a predetermined acceleration rate as a function of the flywheel angular velocity which is proportional to the acceleration rate,

said switching mechanism including:

a control switch operable to indicate functioning of said accelerometer in response to said acceleration rate in operation,

a pair of opposed pivoted gear segments in a fixed position of rest,

an interposed pinion meshing therewith to hold said segments balanced against centrifugal movement, and

means carried by said pinion for operating said control switch in response to extended rotational movement thereof,

said switching mechanism further including:

two centrifugally-movable magnetic plunger elements each connected to pivotally move one of said gear segments, thereby to rotate said pinion and operate said switch, and

magnetic means providing a predetermined magnetic holding force on said plungers to establish an operating threshold for said accelerometer at the predetermined acceleration rate,

means for controlling the seismic mass to permit movement thereof toward the base and rotation of the flywheel to a speed corresponding to said desired acceleration rate at which the magnetic holding means is overcome, thereby to permit the magnetic plunger elements to move centrifugally and the gear segments to rotate the pinion for operation of said control switch and resultant indication of the acceleration rate.

5. An integrating accelerometer as defined in claim 4, wherein the means for controlling the seismic mass in- 50 cludes:

a bias and reset unit mounted on said base and including a cylindrical guide casing in spaced parallel relation to the guide rod and gear rack and a cylindrical plunger element axially movable therein as a biasing mass to establish a bias level of acceleration for operation of the accelerometer, and to reset the seismic mass when the acceleration falls below the bias level,

a bias spring connected with said biasing mass to resiliently hold said mass withdrawn in a position of rest away from the base with a predetermined resistance to movement when subject to acceleration below said desired rate, and

brake means engaging said flywheel and releasable by 65 movement of said biasing mass away from said position of rest.

References Cited by the Examiner UNITED STATES PATENTS 2,522,536 9/1950 Rabinow 20061 3,020,367 2/1962 Bariffi 20061 3,101,002 8/1963 Van Zyl et al. 73-514- BERNARD A. GILHEANY, Primary Examiner. 75 JOSEPH J. BAKER, Assistant Examiner. 

1. IN A INTEGRATING ACCELEROMETER, THE COMBINATION OF A SUPPORTING STRUCTURE INCLUDING A BASE, A GEAR RACK, MOUNTED UPRIGHT ON SAID BASE, A GUIDE ROD MOUNTED UPRIGHT ON SAID BASE IN SPACED PARALLEL RELATION TO SAID GEAR RACK, A SEISMIC MASS INCLUDING A STEP-UP TRAIN, A FLYWHEEL, CENTRIFUGAL SWITCHING MECHANISM CARRIED BY SAID FLYWHEEL AND OPERABLE TO COMPLETE A CONTROL CIRCUIT CONNECTION UPON A PREDETERMINED ROTATIONAL SPEED OF SAID FLYWHEEL, SAID MECHANISM HAVING CENTRIFUGALLYMOVABLY MAGNETIC MEANS FOR ESTABLISHING AN OPERATING THRESHOLD, SAID MASS BEING MOUNTED ON AND MOVABLE ALONG SAID GUIDE ROD UPON ACCELERATION OF SAID MASS IN A DIRECTION NORMAL TO SAID BASE AND AXIALLY OF SAID GUIDE ROD, SAID GEAR TRAIN HAVING A LOW SPEED PINION IN MESH WITH SAID RACK AND A HIGH SPEED PINION ROTATABLE WITH SAID FLYWHEEL TO DRIVE SAID FLYWHEEL AT AN ANGULAR VELOCITY PROPORTIONAL TO A DESIRED ACCELERATION RATE AND VELOCITY, MEANS MOUNTED ON SAID BASE AND INCLUDING A SPOOLED RETRACTING SPRING FOR RESILIENTLY MAINTAING SAID MASS IN A ZERO POSITION SPACED FROM SAID BASE ON SAID ROD WHENM THE ACCELERATION OF SAID ACCELEROMETER IS BELOW A PREDETERMINED BIAS LEVEL AND FOR RESETTING SAID MASS TO SAID ZERO POSITION WHEN SAID ACCELERATION FALLS BELOW SAID BIAS LEVEL, AND A BRAKE SHOE BIASED INTO ENGAGEMENT WITH SAID FLYWHEEL AND RELEASABLE THEREFROM THROUGH CONTACT WITH SAID LAST-NAMED MEANS UPON MOVEMENT OF SAID MASS FROM SAID ZERO POSITION. 